Chapter 9.3: Energy Changes and Chemical Reactions

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Grade 8 Integrated Science Chapter 9 Lesson 3 on energy changes and chemical reactions. An introduction to conservation of mass, endothermic and exothermic reactions, activation energy, and potential …

Grade 8 Integrated Science Chapter 9 Lesson 3 on energy changes and chemical reactions. An introduction to conservation of mass, endothermic and exothermic reactions, activation energy, and potential energy graphs.

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  • 1. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 1 Vocabulary       endothermic (319) – Chemical reactions that absorb thermal energy exothermic (319) – Chemical reactions that release thermal energy activation energy (320) – the minimum amount of energy needed to start a chemical reaction catalyst (322) – a substance that increases reaction rate by lowering the activation energy of a reaction enzyme (322) – a catalyst that speeds up chemical reactions in living cells inhibitor (322) – a substance that slows, or even stops, a chemical reaction Energy Changes  To propel a space shuttle, scientists use rocket fuel.  The shuttle’s main engines burn almost 2 million L of liquid hydrogen and liquid oxygen.  The reaction produces water vapor and a lot of ______________________.  The ___________________energy causes the water vapor to heat to high temperatures.  The rapidly expanding water vapor pushes the shuttle. Chemical Energy in Bonds  Chemical _______________ contain a form of energy called chemical energy o Breaking a bond _______________ energy from the surroundings. o The formation of a bond _________________energy to the surroundings. o Some chemical reactions release more energy then they absorb. o Others absorb more than they __________________. o You can detect these energy changes by recording the _______________________of the surroundings. Endothermic Reactions – Energy Absorbed  Chemical reactions that absorb thermal energy are ___________________ reactions  For an endothermic reaction to continue, __________________must be constantly added.  In these reactions _______________________energy is required to break bonds of the reactant than is released when the products form.  Therefore, the overall reaction _______________________ energy. Draw an energy diagram for an endothermic rxn.
  • 2. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 2 Exothermic Reactions – Energy Released  An ___________________reaction is a chemical reaction that releases thermal energy  In an exothermic reaction, more energy is ____________________when the products form than is required to break the bonds in the reactants.  Therefore, the overall reaction _________________energy Draw an energy diagram for an exothermic rxn. Activation Energy  Many reactions do not start by______________________________. o Paper does not burn when it touches oxygen. _________________is required.  All reactions require _______________________ to start the breaking of bonds.  This is called ______________________ energy.  Activation energy is the ______________________________amount of energy needed to start a chemical reaction. o Different reactions require __________________________activation energies  The rusting of iron is a reaction that has a _________________activation energy. o The energy in the surroundings is enough to start the process.  Other reactions require ___________ energy and have ____________ activation energy o The burning of wood requires the energy of a flame. o Once the reaction starts, the reaction itself ___________________ enough energy to keep the reaction going. Reaction Rates
  • 3. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 3   Some reactions happen quickly, while others happen very ______________________ o Fireworks explode in seconds o The rate of reaction is the __________________________ at which it occurs. For a chemical reaction to occur, particles must collide in the right _____________________ with enough energy to _________________ the bonds o Chemical reactions occur faster of particles collide more often or move faster when they collide. Several Factors Affect Reaction Rates  ___________________________________  ____________________________________  Concentration and Pressure  _________________________________  Inhibitors Surface Area  Surface area is the amount of ______________________, outer area of a solid.  Increased surface area increases reaction rate because more _________________________ on the surface if a solid come into contact with the particles of another substance. o Consider a piece of chalk versus the same amount of chalk powder. Temperature
  • 4. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 4   At higher temperatures, the average __________________________of particles is greater This speeds reactions in two ways o First, particles _____________________ more often o Second, collisions with more _________________________ are more likely to break chemical bonds Concentration and Pressure  Increasing the ________________________________of one or more reactants increases collisions between particles.  More collisions results in a faster reaction rate.  In gases an increase in _________________________________ pushes gas particles closer together  When they are close, more collisions occur
  • 5. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 5 Catalysts  A catalyst is a substance that increases reaction rate by lowering the __________________________energy of a reaction. o One way catalysts speed reactions is by helping reactant particles ___________________________ each other more often o A catalyst isn’t _______________________ in a reaction, and it doesn’t change the reactants or products o A catalyst doesn’t increase the amount of reactant used or the amount of product that is made.  Catalyst are not_______________________, so they are not considered reactants  Your body is filled with catalysts called_______________________________.  An enzyme is a catalyst that speeds up chemical reactions in living cells. o The enzyme protease breaks the protein molecules that can be absorbed by your intestine. o Without protease the reaction would occur too slowly and we could not_________________________.
  • 6. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 6 Draw an energy diagram of a catalyzed and uncatalyzed reaction. Inhibitors  An inhibitor is a substance that____________________________, or even stops, a chemical reaction caused by an enzyme.  Inhibitors are often used on our foods. ________________________________ are inhibitors that slow the processes that cause food to spoil.